This invention relates to improvements in metering devices, and particularly to metering devices used in agricultural and horticultural spraying devices and related application equipment.
Sprayers are used in agriculture and horticulture for applying chemicals and/or liquid fertilisers to growing crops, and for the treatment of harvested produce.
Generally, sprayers have a series of outlets across the width of the sprayer boom. Each outlet through which liquid is passed is provided with a check valve, commonly known as an Anti Drip Check Valve, and the check valve is generally equipped with a means to attach a nozzle or applicator on the downstream side of the check valve. Check valves are provided to prevent liquid flowing from the outlets when the said liquid is below a predetermined pressure. For example, a check valve may be set up so that liquid may not pass through the valve unless the liquid is at the intended working or application pressure.
Check valves are available in various different forms. The most common type used in agricultural and horticultural sprayers comprises a sealing diaphragm maintained against a sealing face by a compressed coil spring, the spring rate, or loading of which is determined by the pressure at which the valve is required to open and the surface area of the sealing diaphragm.
In practice when the supply pressure to the sprayer boom is switched off, the pressure in the boom supply line drops and when below the level at which it exerts sufficient force to maintain the spring loaded diaphragm check valve in an open position, the valve shuts. The length of time taken for the line pressure to drop after shut off can be lengthy, and increases as higher spraying pressures are used. Given the characteristics of the spring loaded diaphragm check valve they are not generally used in high pressure sprayer applications.
In another type of check valve, a ball loaded against an annular sealing face by a coil spring is used. Ball type check valves are generally used where sprayers are operated at higher pressures, because unlike the spring loaded diaphragm check valve their sensitivity is not dependent on, or effected by, pressure acting over a large surface area to withhold the ball from the point of sealing and therefore provide outlets with a quicker shut off.
Where high spraying pressures are to be used, it is common to provide a spring loaded check valve downstream of a spring loaded diaphragm valve to facilitate quick shut off of the outlet and manufacturers of check valves as described commonly accommodate such practice by providing suitable fittings to their check valve products.
Certain crops, ground conditions, weather conditions or chemicals require different operating pressures to be used necessitating switching over from a high pressure application to a low pressure application and vice versa. This causes time delays due to the assembly and disassembly of components. There is also a risk of components being mixed up and the operator being contaminated with toxic chemical.
Passive check valves, be they diaphragm or ball valves, share a common problem. The problem is that a time delay exists between the moment at which the liquid supply is turned off at source, and the time at which the pressure in the boom drops sufficiently for the check valves to operate and so prevent the flow of liquid from the outlets. The further away from the centre of the boom a particular nozzle is, the longer is the time delay. At present, sprayers having booms of 24 meters are often used. When operating at 2.5 to 3.0 bar and depending on the spray nozzles fitted downstream of the outlet, an operator may observe a time delay of ten seconds between shutting off liquid flow, and liquid ceasing to flow through the outlets. This causes crop damage due to patches of crop being overdosed which in turn may lead to environmental damage, and is of course a waste of valuable resource. For example, a sprayer travelling at 12 km/h may travel 33 meters in the interval between the operator shutting off the flow of liquid and the outlets actually being closed off. There is a particular problem found in brassica crops when turning at headlands. This is because brassica crops are very sensitive to chemicals and at row ends and headlands some of the crop will almost inevitably be double dosed. This has led farmers to leave field headlands unplanted which represents a considerable reduction in effective land usage.
In some countries stringent environmental protection laws have been introduced to limit the application of chemicals, such as fungicides, herbicides, pesticides or fertilisers, per unit area in given time periods in order to reduce the risk of ground water being contaminated by the said chemicals. The potential liabilities, in terms of penalties, resulting from double dosing caused by inaccurate shut-off valves is therefore of prime concern to the farmer.
A further problem posed by spring operated check valves is that operating performance is governed by the accuracy of the springs fitted within them. Coil springs are manufactured in a manner whereby the spring ratings have wide tolerances. Where springs are designed to operate check valves at 1.0 bar for instance, due to the tolerance in the spring rating one check valve may not open until a pressure of 1.1 bar is reached, whilst the check valve in an adjacent outlet may open at a pressure of 0.8 bar. Clearly, in the precision application of chemicals and fertilisers this is most undesirable.
In the spraying of liquid fertilisers it is desirable to operate at low pressures. This is because higher pressures produce fine droplets in the form of a mist which may remain on the leaves of the plants and lead to burning of the crop. In order to produce large droplets, lower pressures must be used. Conventional check valves limit the lower range of operating pressures since spring operated check valves do not operate reliably below 1 bar. Whilst liquid fertiliser can be applied at 1 bar it is desirable to operate at even lower pressures.
It would therefore be desirable to provide a check valve having controllable shut-off which can be opened at low operating pressures and which has very fine tolerances on its opening and closing pressures.
Spring loaded diaphragm check valves of the type so far described pose additional problems to users. At the time the sprayer boom is folded for transport, and/or during normal transport to or from the site of spraying, any liquid remaining in the boom supply lines tends to surge, as a result of movement, which causes localised increases in internal pressure sufficient to open the check valve and thereby allow liquid to escape. Such escape can lead to unintended contact with other crops as the sprayer passes by, double dosing or worse spraying the operator or passers by who become contaminated with toxic chemical. Such escape would permit corrosive solutions to come into contact with the sprayer, and this is particularly damaging in the case where the liquid is fertiliser. It would therefore be desirable to provide a check valve which may be adjusted to open and close at any desired pressure. It Is also desirable to provide a check valve having its shut off at a pressure closely adjacent to the operating pressure of the sprayer, which pressure may vary with time, and would therefore allow the pressure in the supply to the inlet to remain at a level close to the operating pressure required when spraying is resumed. Such a feature would reduce the time taken for full operating pressure to be achieved when the operator switches a sprayer back on when re-entering a crop.
As mentioned above, generally, sprayers have a series of outlets across the width of the sprayer boom. Each outlet through which liquids are passed is generally provided with a check valve which is generally equipped with a means to attach a nozzle or applicator on the downstream side of the check valve. The nozzle or applicator distributes the flow of liquid in a manner specific to the desired or most appropriate application method for the given chemical or fertiliser and is generally selected by the operator who takes into account the liquid being applied as well as crop and weather conditions and intended speed of application. In many cases the nozzle or applicator design is such that the outlet design regulates the flow of liquid and at the same time disperses the liquid in an optimum fashion. For example, a fan jet nozzle will regulate the flow of liquid dependent of the liquid pressure and then distribute the liquid in droplets of a particular size and density in a fan shaped pattern.
There are nozzles and applicators which do not embody the same characteristics as the type previously describes, and which therefore require additional and separate methods of regulating or metering the flow so as to provided a necessary control on the volume of liquid flowing from the particular sprayer outlet. In different applications it may be necessary to apply different volumes of liquid. In order to provide for this metering discs or nozzles are used, the metering discs generally fitting between the nozzle or applicator attaching means and the outlet or the outlet of the check valve. When applying liquid fertiliser with a dribble bar, a metering disc is used.
A metering disc generally has an aperture in its centre, the diameter of the aperture providing for a range of application volumes over the range of pressures for which the nozzle or applicator is designed to operate. When the limits of the range are reached, it is necessary to change the metering valve for another having a differently sized aperture.
There are many different sized metering discs or orifices available, typically however, to cover the requirements of most agricultural and horticultural applications three different metering discs are needed for any one nozzle or applicator. The time taken to change the metering disc for each outlet is great, and as the size of booms tends to increase so does the significance of the time taken to change metering discs/nozzles.
It would therefore be desirable to provide a metering mechanism which does not require the changing of metering discs and which provides a range of metering which spans most commonly used application rates.
The invention provides a check valve comprising a body having an inlet and an outlet, an inlet chamber and an outlet chamber mounted in the said body between the inlet and the outlet, the said inlet chamber being provided with a check valve to permit or prevent the flow of liquid from the inlet chamber to the outlet chamber, the check valve comprising a diaphragm and pressurising means to exert a pressure on the said diaphragm, wherein the pressurising means provides for a variable pressure to be exerted on the said diaphragm.
One aspect of the invention provides a kit of parts comprising a diaphragm and pressurising means to exert a pressure on the said diaphragm when said diaphragm is attached to a check valve comprising a body having an inlet and an outlet, an inlet chamber and an outlet chamber mounted in the said body between the inlet and the outlet, the said inlet chamber being provided with a check valve to permit or prevent the flow of liquid from the inlet chamber to the outlet chamber, wherein the pressurising means provides for a variable pressure to be exerted on the said diaphragm.
The pressurising means may be pneumatic, or hydraulic. Alternatively. the pressurising means may comprise an electrically or electronically activated actuator, such as a solenoid.
The pressurising means may exert a pressure in the range 0.3 Bar to 6 Bar on the diaphragm.
In another embodiment of the invention, the pressurising means may exert a pressure of up to 20 Bar. Such high pressures are often used in aerial crop spraying.
Advantageously, the diaphragm is formed from an elastomeric material, and preferably the thickness of the diaphragm is between 0.5 and 1.5 mm.
Preferably, the diaphragm is held in place by an end cap. The end cap and the body may be provided with co-operating attachment means. The attachment means may be a bayonet fitting, or screw threads.
In one embodiment of the invention, the cap comprises an aperture and a nozzle to which an air or hydraulic supply may be attached.
Where the pressurising means is hydraulic or pneumatic the diaphragm may be pre-shaped and/or pre-stressed so that as the pressure exerted by the pressurising means decreases the diaphragm lifts away from its sealing position. Preferably, the diaphragm is pre-stressed so that in a resting position it is in compression. Advantageously, the diaphragm is very thin in cross-section.
The combination of a diaphragm which is both thin and pre-shaped and/or pre-stressed results in a diaphragm that is very sensitive and which responds very quickly to changes in pressure exerted on the diaphragm by the pressurising means, thereby enabling fast and accurate shut off or opening of fluid flow from the inlet to the outlet of the check valve.
The outlet chamber may comprise a pipe which extends within the inlet chamber.
A dribble bar, or any other suitable nozzle, may be attached to the outlet, and the body of the valve may be adapted to provide for such attachment.
In one embodiment of the invention there is provided a detection and control means to detect the fluid pressure in the body of the valve and adjust the pressure exerted by the pressurising means in response to the detected fluid pressure thereby providing shut off pressures which are in close proximity to actual operating pressures. The fluid pressure may be detected in the inlet chamber or the supply to the inlet. The pressure exerted by the pressurising means may follow the fluid spraying pressure, so that the pressure exerted by the pressurising means on the diaphragm is only fractionally greater or less than the spraying fluid pressure.
The control means may be adapted to cause the pressurising means to exert sufficient pressure to cause shut off of the check valve when the fluid pressure falls below a pre-set value. The control means may be arranged to exert a pressure on the diaphragm which is proportional to the fluid pressure detected. Alternatively, the control means may be arranged to exert a pressure on the diaphragm which is a greater or less than the fluid pressure by a fixed amount, e.g. 0.5 bar greater or less than the fluid pressure.
The invention provides a rotary metering valve comprising a metering block having an inlet connectable to a fluid supply and at least one outlet, and an outlet selector having at least one aperture therein for alignment with an outlet of the metering block to permit flow of a fluid therethrough, wherein the outlet selector and the metering block are arranged to permit relative rotation of one with respect to the other, and a means to rotate the outlet selector and/or the metering block.
The metering block may be cylindrical. The outlet selector may be cylindrical.
Typically the outlet selector is arranged to envelop a portion of the metering block, or to be enveloped by a portion of the metering block.
The metering block may be provided with a plurality of outlets and the outlet selector is provided with one aperture. The metering block is suitably provided with three outlets. The metering block may be provided with one outlet and the outlet selector may be provided with a plurality of outlets. The metering block may be provided with a plurality of outlets and the outlet selector may be provided with a plurality of apertures. The or each outlet of the metering block may comprise a bore in a wall thereof. Where more than one outlet is provided in the metering block, the sizes of the outlets may differ. Where more than one aperture is provided in the outlet selector, the sizes of the apertures may differ.
The metering block may be fixed and the outlet selector may rotate relative to the said metering block. Alternatively, the outlet selector may be fixed and the metering block may rotate relative to the said outlet selector.
The metering block may be secured in a body. Preferably, the outlet selector fits over the metering block, and more preferably, a cap holds the metering block and the outlet selector in position within the body. The cap may be held in place by screw threads, a bayonet fitting, or other suitable attachment means. The cap may sit against an external flange.
Preferably, the cap has a portion through which part of the outlet selector extends, seals such as xe2x80x9cOxe2x80x9d rings being provided to prevent egress of fluid from within the body through the cap.
The metering block and outlet selector assembly may be mounted in a body, which body may be provided with at least one outlet. The body may comprise multiple outlets and may be substantially cylindrical. The body is suitably a dribble bar having multiple outlets.
In certain circumstances instead of an equal amount of liquid flowing from each of the body""s outlets a different amount of fluid can flow from each outlet. This can be due to a rotational flow occurring between the inner wall of the body and the metering block and outlet selector assembly.
In one embodiment of the invention a barrier is provided between an inner surface the body and the metering block and outlet selector assembly. The barrier may extend from an inner wall of the body to the metering block and outlet assembly. The barrier may abut the outlet selector or the metering block. The barrier serves to balance and break flow of a rotational nature and is so formed to enable the accurate division of liquid between the outlets in the body.
Advantageously, the barrier is so located and dimensioned as to provide for an accurate division of liquid between the outlets in the body, the flow through each outlet being within the tolerance requirements for constancy of flow from singularly fed nozzles having multiple outlets as set out in national, international or industry standards and codes.
The barrier may be aligned with an axial centre line of the body, outlets being located to either side of the centre line. An equal number of outlets may be provided on either side of the said centre line.
In another embodiment of the invention, the number of outlets to either side of the centre line may be unequal, and the barrier may be positioned in the body to ensure that the flow to each outlet is equal.
The position of the barrier with respect to the outlet of the outlet selector and metering block assembly into the body can also effect the flow from the outlets in the body. The barrier may be aligned with the outlet of the outlet selector and metering valve assembly, or the barrier may be off-set from the outlet of the outlet selector and metering valve assembly.
The means to rotate the outlet selector may be a hand grip, lever, or spanner flats, and the said means may be provided on the part of the outlet selector which extends through the cap.
Alternatively, the means to rotate the outlet selector and/or the metering block may comprise an actuator, which actuator may be activated remotely, for example by a controller.
The body may be part of an outlet fitting for a sprayer or may be part of the nozzle which attaches to a sprayer outlet through which fluid finally leaves the sprayer.
Preferably the metering block is formed from stainless steel or suitable polymers or thermoplastics, which may be of the type known as engineering plastics. Alternatively, the metering block may be formed from brass, ceramics or other suitable materials.
The outlet selector and/or the body may be formed from a polymer or thermoplastic. Alternatively, the outlet selector and/or the body may be formed from machined or cast ferrous or non ferrous materials.
One aspect of the invention provides a valve assembly comprising a check valve comprising a body having an inlet and an outlet, an inlet chamber and an outlet chamber mounted in the said body between the inlet and the outlet, wherein the inlet chamber there is provided with a diaphragm which permits or prevents the flow of liquid from the inlet chamber to the outlet chamber, and pressurising means to exert a pressure on the said diaphragm, and the outlet chamber being provided with a rotary metering valve comprising a metering block having an inlet connectable to a fluid supply and at least one outlet, and an outlet selector having at least one aperture therein for alignment with an outlet of the metering block to permit flow of a fluid therethrough, the outlet selector and the metering block being arranged to permit relative rotation of one with respect to the other, and a means to rotate the outlet selector and/or the metering block is provided.
Preferably, the diaphragm is provided at upstream end of the inlet chamber.
The pressurising means may be hydraulically, pneumatically, electrically or mechanically operated. For example, the diaphragm may be held against a sealing face by means of a spring.
Advantageously, the rotary metering valve is attached to the downstream end of the outlet chamber.
The pressurising means may permit a variable pressure to be exerted on the said diaphragm.
According to another aspect of the invention, there is provided a sprayer having a check valve and/or a metering valve according to the invention.
In one embodiment of the invention, the control means may communicate with a satellite derived or computer generated mapping system, shutting off and opening one or more of the valves, and/or adjusting one or more rotary metering valve in accordance with information received from the said mapping system. The rotary metering valves may be motorised to enable them to be adjusted in response to a signal from the said mapping system.
The invention provides a metering valve which does not require disassembly in order to adjust the size of the aperture through which the liquid passes.
In one embodiment of the invention check valves according to the invention are controlled as a group in order to control fluid flow from individual sections of a sprayer boom. By using check valves in this manner, the use of mechanical fluid control valves, to shut off fluid being supplied to individual sections of a sprayer boom is not required. The arrangement also permits the sprayer to be equipped with one single feed line for the spray boom as opposed to sprayers of the prior art which have a plurality of fluid supply lines, the number of supply lines corresponding to the number of sections on the boom.
Another embodiment of the invention provides a sprayer comprising a tank provided with a feed line which extends from and returns to the tank, wherein the feed line is provided a valve to control the return of fluid in the feed line to the tank. Advantageously, the sprayer is provided with a controller and the said valve is controlled by the controller.
The sprayer is preferably provided with a pressure regulator which maintains the pressure in the feed line constant.
Preferably, the valve is a check valve according to the invention. The check valve may comprise a rotary metering valve according to the invention.
Alternatively, the valve may be a regulating valve such as a rotary valve, or a gate valve.
The provision of this feature allows chemical solutions to circulate constantly through the feed lines of sprayer boom even when the sprayer is not operating, so that the chemical remains mixed and available to the outlets at the required spraying pressure at all times. The re-circulation of liquid suspensions such as fertilisers is extremely desirable to ensure that they are applied to crops in a consistent solution and this feature provides a means of achieving this.
The valve provided in the feed line to control the return of fluid in the feed line to the tank may be used to allow recirculation during spraying. Where the valve is a check valve according to the invention the outlet of the valve may be of a size which permits a desired re-circulatory flow rate when the check valves controlling the flow of fluid through the sprayer nozzles are open. By combining a rotary metering valve with the check valve, different re-circulatory flow rates can be provided for. Alternatively, a regulating valve may be used in the feed line. In each case the position of the valve may be controlled by the controller.
Another benefit of the valve in the feed line to control the return of fluid in the feed line to the tank, is that a further means of controlling the flow rate of fluid through the sprayer nozzles is provided. This is because a proportion of fluid which would have passed through the nozzles is being returned to tank.
The check valve of the invention enables the time delay during the build up to operating pressure following check valve shut-off and resumption of spraying to be kept to a minimum. The speed at which the check valve operates can be adjusted by varying the pressure exerted on the diaphragm by the pressurising means. Increasing the pressure increases the speed of operation of the check valve.
Due to the absence of mechanical springs, the check valve of the invention does not suffer from variance in tolerance of spring ratings, and therefore is much safer and more accurate than presently available check valves, both in terms of crop and environmental damage. Furthermore, when used on a sprayer, where it is necessary to change the operating pressure thereof, rather than physically changing springs or actual check valves, the degree to which the diaphragm is pressurised may simply be adjusted either manually or by a control system as described herein.
The metering devices of the invention may be used in many different applications, but are particularly suited for use with agricultural and horticultural spraying machines. Furthermore, the metering devices of the invention can be supplied as integral components within nozzles or applicators which are fitted to spraying machines or as integral parts within check valve assemblies which may be retro-fitted to existing sprayers. Retro-fit kits may use existing outlet fittings and in the case of a check valve replaces the spring with a pressurising means of the invention, or in the case of a rotary metering valve replaces the metering disc.